Epoxy resins are used for adhesives, molding materials, coating materials, photoresist materials, color developing materials, etc., and in view of the excellent heat resistance and moisture resistance of resultant cured products, epoxy resins are widely used in the electric and electronic field such as a semiconductor encapsulant, an insulating material for a printed circuit board, etc.
Among these various applications, in the field of printed circuit boards, the tendency toward higher densities due to narrowing of the wiring pitches of semiconductor devices becomes remarked with miniaturization and improvement in performance of electronic apparatuses. As a semiconductor mounting method corresponding to this, a flip-chip bonding method of bonding a semiconductor device and a substrate with solder balls is widely used. The flip-chip bonding method is a so-called reflow-system semiconductor mounting method in which solder balls are disposed between a circuit board and a semiconductor and the whole is heated to cause fused-junction between the circuit board and the semiconductor. Therefore, the circuit board is exposed to a high-heat environment during solder reflowing, and thus large stress occurs in the solder balls, which are used for bonding together the circuit board and the semiconductor, due to thermal contraction of the circuit board, thereby causing faulty connection in wiring. Therefore, a low-thermal-expansion material is required as an insulating material used for printed circuit boards.
In addition, high-melting-point solder not using lead has become a main stream by the legal regulations for environmental problems. The lead-free solder is used at a temperature about 20 to 40° C. higher than that for usual eutectic solder, and thus a curable resin composition is required to have higher heat resistance.
Printed circuit boards are generally manufactured by curing and molding curable resin compositions, each of which contains an epoxy resin as a main component, integral with glass woven fabrics, and improvements in epoxy resins are required for achieving higher heat resistance and lower thermal expansibility.
In order to comply with these requirements, for example, a naphthalene-type epoxy resin produced by condensation of a naphthol compound with formaldehyde and then reaction with epichlorohydrin is known as a material capable of resolving the technical problems of heat resistance etc. (refer to Patent Literature 1 below).